Meanwhile, possibly due to Derby's connections, Hawkins was appointed assistant superintendent of the Great Exhibition of 1851 in London. The following year (1852), he was appointed by the Crystal Palace company to create 33 life-size concrete models of extinct dinosaurs to be placed in the south London park to which the great glass exhibition hall was to be relocated. In this work, which took some three years, he collaborated with Sir Richard Owen and other leading scientific figures of the time – Owen estimated the size and overall shape of the animals, leaving Hawkins to sculpt models according to Owen's directions (one, Iguanodon, was so large that a 20-strong dinner party was held inside on 30 December1853).

Hawkins was later commissioned to produce models for New York City's Central Park museum similar to these he had created in Sydenham. He established a studio on the modern site of the American Museum of Natural History in Manhattan, and planned to create a "Paleozoic Museum". However, corrupt local politics intervened, the project was shelved in 1870, and the models that Hawkins had created were said to have been buried somewhere in Central Park.

Hawkins then turned to dinosaur skeleton reconstruction work at the Smithsonian Institution in Washington, at Princeton University [then called the College of New Jersey] in Princeton, New Jersey (where he also created paintings of dinosaurs), and for the Centennial Exhibition of 1876 in Philadelphia before returning to Britain in 1878, where he died.